This is one of a few cases where the tested and working mechanics inside the skills are shown incorrect in the stats. Trust me please when i say that the slowing means slowing down and that indeed the DA of the monsters is reduced.
The stats in the hud are automatically assembled by TQ, i didnt write them. And some stats are just shown in a confusing way or outright incorrect, like in this case.
Please consider it a TQ-bug as for now. I shall see if i can hack a bit deeper into the hud-system once i have the easier things fixed.
Thanks